Method for producing highly functional, hyper branched polyester by means of enzymatic esterification

ABSTRACT

The present invention relates to a process for preparing highly functional hyperbranched polyesters which comprises reacting a reaction solution comprising solvent and
     (a) one or more dicarboxylic acids or one or more derivatives thereof with one or more at least trifunctional alcohols   (b) or one or more tricarboxylic acids or higher polycarboxylic acids or one or more derivatives thereof with one or more diols   (c) or one or more tricarboxylic acids or higher polycarboxylic acids or one or more derivatives thereof with one or more at least trifunctional alcohols   (d) or one or more di- or polyhydroxycarboxylic acids   (e) or one or more hydroxydi- or hydroxypolycarboxylic acids   or mixtures of at least two of the above reaction solutions
 
in the presence of an enzyme at temperatures above 60° C. and pressures above 500 mbar.

The present invention relates to a process for preparing highlyfunctional hyperbranched polyesters which comprises reacting a reactionsolution comprising solvent and

-   (a) one or more dicarboxylic acids or one or more derivatives    thereof with one or more at least trifunctional alcohols-   (b) or one or more tricarboxylic acids or higher polycarboxylic    acids or one or more derivatives thereof with one or more diols-   (c) or one or more tricarboxylic acids or higher polycarboxylic    acids or one or more derivatives thereof with one or more at least    trifunctional alcohols-   (d) or one or more di- or polyhydroxycarboxylic acids-   (e) or one or more hydroxydi- or hydroxypolycarboxylic acids-   or mixtures of at least two of the above reaction solutions    in the presence of an enzyme at temperatures above 60° C. and    pressures above 500 mbar.

The present invention further relates to highly functional hyperbranchedpolyesters obtainable by the process described above and to the use ofthe resulting highly functional hyperbranched polyesters in coatings,paints, coverings, and adhesives.

Modified highly functional hyperbranched polyesters and polyester-baseddendrimers are known per se from WO 96/19537, for example, and arealready used in some applications, as impact modifiers, for example. Butdendrimers are too expensive for general use, since the syntheses areexacting in their need for high yields in the constructional reactionsand high purity in the intermediates and end products, and employreagents which are too expensive for large-scale industrial use. Thepreparation of hyperbranched highly functional polyesters prepared byconventional esterification reactions normally requires very drasticconditions (cf. WO 96/19537) such as high temperatures and/or strongacids, for example. As a result, there may be side reactions such asdehydration reactions and decarboxylations, for example, and as aconsequence of the side reactions there may be instances of unwantedresinification and discoloration.

Known esterification processes which are able to take place under gentleconditions include on the one hand those using very expensive activatingreagents, such as dicyclohexylcarbodiimide, and using protective groupchemistry, which is uneconomic in large-scale industrial reactions, andon the other hand enzymatic reactions, which do not provide the desiredproducts, however. For instance, GB 2 272 904 discloses a process forthe lipase-catalyzed preparation of a polyester by reacting at least onealiphatic dicarboxylic acid with at least one aliphatic diol or polyolor reacting at least one aliphatic hydroxycarboxylic acid with itself toform polyesters. The process is conducted at temperatures from 10 to 60°C., preferably from 40 to 45° C., and even when using glycerol givespreferentially unbranched polyesters (page 3 lines 26/27). The processdisclosed in GB 2 272 904 can therefore be used for the targetedsynthesis of linear polymers. Pentaerythritol cannot be reacted inprocesses disclosed in GB 2 272 904 (page 3 line 28). The exampledemonstrates the synthesis of a linear polyester from adipic acid andbutane-1,4-diol.

WO 94/12652 discloses a process for enzyme-catalyzed synthesis ofpolyesters which is conducted in the absence of solvents (page 3 line26). Two steps can be distinguished. In the first, oligomers areprepared enzymatically from diols and dicarboxylic acids or relatedproducts. Thereafter, either the enzyme is recovered and the reaction iscontinued at elevated temperature or the enzyme is left in the reactionmixture and the temperature is raised, with the risk of possibleirreversible destruction of the enzyme.

In WO 98/55642 a special process for enzyme-catalyzed synthesis ofpolyesters by reacting either hydroxycarboxylic acids or else aliphaticdicarboxylic acids with aliphatic diols or polyols and, optionally, analiphatic hydroxycarboxylic acid in a two-stage process, in the firststage of which—optionally in the presence of water—the starting productsare reacted in the molar ratio of from 1:1 to 1.1:1 and, before thesecond stage, the supported enzyme is removed and recycled, the secondstage being conducted at elevated temperature. The process discloseddoes not effect reaction of sterically hindered secondary hydroxylgroups (page 7 lines 27/28), with the secondary hydroxyl group ofglycerol, for example, being classed as sterically hindered (page 8 line4), so that reaction of glycerol gives linear products.

WO 99/46397 discloses the synthesis of polyesters by reacting, forexample, a polyol having two primary and at least one secondary alcoholfunction(s) with one or more dicarboxylic or tricarboxylic acids in thepresence of an effective amount of a lipase, carried out preferablyunder reduced pressure, so that linear polyesters are obtained.

L. E. Iglesias et al. report in Biotechnology Techniques 1999, 13, 923that linear polyesters are obtained by esterifying glycerol with adipicacid in the presence of an enzyme at 30° C.

B. I. Kline et al. report in Polymer Mat. Sci. Eng. 1998, 79, 35 thatlinear polyesters are obtained by reacting glycerol with divinyl adipatein the presence of an enzyme at 50° C.

On a poster at “The Second International Dendrimer Symposium”, ids-2,Oct. 14–17, 2001, Tokyo University, Japan, H. Uyama reported theformation, during the reaction of polyazelaic anhydride with glycerol inthe presence of Candida antarctica at 60° C. without solvent, first oflinear oligomers. After 3 days a sharp increase in molecular weight wassuddenly observed, and after 7 days the authors obtained a hyperbranchedpolyester having a molecular weight of 34,000 g/mol. Such drasticchanges in the course of the reaction are, however, undesirable inlarge-scale industrial reactions, since they can lead to the reactionsgoing out of control.

It is an object of the present invention to provide a process forpreparing highly functional hyperbranched polyesters which avoids thedisadvantages known from the prior art and prevents changes, especiallyuncontrolled changes, in reaction conditions. A further object is toprovide novel highly functional hyperbranched polyesters. A last objectis to provide novel uses for highly functional hyperbranched polyesters.

We have found that this object is achieved by the process defined at theoutset.

The process of the invention comprises reacting reacting a reactionsolution comprising

-   (a) one or more dicarboxylic acids or one or more derivatives    thereof with one or more at least trifunctional alcohols-   (b) or one or more tricarboxylic acids or higher polycarboxylic    acids or one or more derivatives thereof with one or more diols-   (c) or one or more tricarboxylic acids or higher polycarboxylic    acids or one or more derivatives thereof with one or more at least    trifunctional alcohols-   (d) or one or more di- or polyhydroxycarboxylic acids-   (e) or one or more hydroxydi- or hydroxypolycarboxylic acids    or mixtures of at least two of the above reaction solutions.

High-functionality hyperbranched polyesters for the purposes of thepresent invention are molecularly and structurally nonuniform. Theydiffer in their molecular nonuniformity from dendrimers and aretherefore much less complicated to prepare.

Dicarboxylic acids which can be reacted in reaction solutions accordingto variant (a) include for example oxalic acid, malonic acid, succinicacid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaicacid, sebacic acid, undecane-α,ω-dicarboxylic acid,dodecane-α,ω-dicarboxylic acid, cis- andtrans-cyclohexane-1,2-dicarboxylic acid, cis- andtrans-cyclohexane-1,3-dicarboxylic acid, cis- andtrans-cyclohexane-1,4-dicarboxylic acid, cis- andtrans-cyclopentane-1,2-dicarboxylic acid, and cis- andtrans-cyclopentane-1,3-dicarboxylic acid,

-   which dicarboxylic acids may be substituted by one or more radicals    selected from-   C₁–C₁₀-alkyl groups, examples being methyl, ethyl, n-propyl,    isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl,    isopentyl, sec-pentyl, neopentyl, 1,2-dimethylpropyl, isoamyl,    n-hexyl, isohexyl, sec-hexyl, n-heptyl, isoheptyl, n-octyl, n-nonyl,    and n-decyl,-   C₃–C₁₂-cycloalkyl groups, examples being cyclopropyl, cyclobutyl,    cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl,    cyclodecyl, cycloundecyl, and cyclododecyl; cyclopentyl, cyclohexyl,    and cycloheptyl are preferred;-   alkylene groups such as methylene or ethylidene, or-   C₆–C₁₄-aryl groups such as phenyl, 1-naphthyl, 2-naphthyl,    1-anthryl, 2-anthryl, 9-anthryl, 1-phenanthryl, 2-phenanthryl,    3-phenanthryl, 4-phenanthryl, and 9-phenanthryl, for example,    preferably phenyl, 1-naphthyl, and 2-naphthyl, with particular    preference phenyl.

Exemplary representatives of substituted dicarboxylic acids include2-methylmalonic acid, 2-ethylmalonic acid, 2-phenylmalonic acid,2-methylsuccinic acid, 2-ethylsuccinic acid, 2-phenylsuccinic acid,itaconic acid, and 3,3-dimethylglutaric acid.

The dicarboxylic acids which can be reacted according to variant (a)further include ethylenically unsaturated acids such as maleic acid andfumaric acid, for example, and aromatic dicarboxylic acids such asphthalic acid, isophthalic acid or terephthalic acid, for example.

Additionally, mixtures of two or more of the abovementionedrepresentatives may be used.

The dicarboxylic acids may be used either per se or in the form ofderivatives.

By derivatives are meant preferably

-   -   the corresponding anhydrides in monomeric or polymeric form,    -   mixed anhydrides with other carboxylic acids, such as with        acetic acid,    -   monoalkyl or dialkyl esters, preferably monomethyl or dimethyl        esters or the corresponding monoethyl or diethyl esters, but        also the monoalkyl and dialkyl esters derived from higher        alcohols such as n-propanol, isopropanol, n-butanol, isobutanol,        tert-butanol, n-pentanol, and n-hexanol, for example,    -   monovinyl and divinyl esters, and    -   mixed esters, preferably methyl ethyl esters.

In the context of the present invention it is also possible to use amixture of a dicarboxylic acid and one or more of its derivatives. It isalso possible in the context of the present invention to use a mixtureof two or more different derivatives of one or more dicarboxylic acids.

Particular preference is given to using succinic acid, glutaric acid,adipic acid, phthalic acid, isophthalic acid, terephthalic acid or theirmonomethyl or dimethyl esters. Very particular preference is given tousing adipic acid. Very particular preference is likewise given to usingcommercially available mixtures of succinic, glutaric, and adipic acid.

At least trifunctional alcohols include for example glycerol,butane-1,2,4-triol, n-pentane-1,2,5-triol, n-pentane-1,3,5-triol,n-hexane-1,2,6-triol, n-hexane-1,2,5-triol, n-hexane-1,3,6-triol,trimethylolbutane, trimethylolpropane or ditrimethylolpropane,trimethylolethane, pentaerythritol or dipentaerythritol; sugar alcoholssuch as mesoerythritol, threitol, sorbitol or mannitol, for example, ormixtures of the at least trifunctional alcohols given above. It ispreferred to use glycerol, trimethylolpropane, trimethylolethane, andpentaerythritol.

Examples of tricarboxylic or polycarboxylic acids which can be used inreaction solutions according to variant (b) include1,2,4-benzenetricarboxylic acid, 1,3,5-benzenetricarboxylic acid,1,2,4,5-benzenetetracarboxylic acid, and mellitic acid.

The tricarboxylic or polycarboxylic acids may be used either per se orelse in the form of derivatives.

By derivatives are meant preferably

-   -   the corresponding anhydrides in monomeric or polymeric form,    -   mixed anhydrides with other carboxylic acids, such as with        acetic acid,    -   monoalkyl, dialkyl or trialkyl esters, preferably monomethyl,        dimethyl or trimethyl esters or the corresponding monoethyl,        diethyl or triethyl esters, but also those monoesters, diesters        and triesters derived from higher alcohols such as n-propanol,        isopropanol, n-butanol, isobutanol, tert-butanol, n-pentanol,        and n-hexanol, for example, and monovinyl, divinyl or trivinyl        esters,    -   and mixed methyl ethyl esters.

In the context of the present invention it is also possible to use amixture of a tricarboxylic or polycarboxylic acid and one or more of itsderivatives. It is likewise possible in the context of the presentinvention to use a mixture of two or more different derivatives of oneor more tricarboxylic or polycarboxylic acids.

Diols for reaction solutions according to variant (b) of the presentinvention include for example ethylene glycol, propane-1,2-diol,propane-1,3-diol, butane-1,2-diol, butane-1,3-diol, butane-1,4-diol,butane-2,3-diol, pentane-1,2-diol, pentane-1,3-diol, pentane-1,4-diol,pentane-1,5-diol, pentane-2,3-diol, pentane-2,4-diol, hexane-1,2-diol,hexane-1,3-diol, hexane-1,4-diol, hexane-1,5-diol, hexane-1,6-diol,hexane-2,5-diol, heptane-1,2-diol 1,7-heptanediol, 1,8-octanediol,1,2-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,2-decanediol,1,12-dodecanediol, 1,2-dodecanediol, 1,5-hexadiene-3,4-diol,cyclopentanediols, cyclohexanediols, inositol and derivatives,2-methyl-2,4-pentanediol, 2,4-dimethyl-2,4-pentanediol,2-ethyl-1,3-hexanediol, 2,5-dimethyl-2,5-hexanediol,2,2,4-trimethyl-1,3-pentanediol, pinacol, diethylene glycol, triethyleneglycol, dipropylene glycol, tripropylene glycol, polyethylene glycolsHO(CH₂CH₂O)_(n)—H or polypropylene glycols HO(CH[CH₃]CH₂O)_(n)—H ormixtures of two or more representatives of the above compounds, with nbeing an integer and n=4. One or both hydroxyl groups in theabovementioned diols may also be substituted by SH groups. Preference isgiven to ethylene glycol, propane-1,2-diol, and diethylene glycol,triethylene glycol, dipropylene glycol, and tripropylene glycol.

Reaction solutions which can be reacted according to variant (c)comprise for example one or more triols and one or more tetracarboxylicacids or one or more derivatives thereof. According to variant (c) it isalso possible to react one or more tricarboxylic acids or one or morederivatives thereof with one or more tetrafunctional alcohols. Thereaction of a trifunctional alcohol with a tricarboxylic acid orderivatives is accomplished by the process of the invention preferablywhen the hydroxyl groups or the carboxyl groups differ greatly from oneanother in reactivity.

The molar ratio of hydroxyl to carboxyl groups in variants (a) to (c)are from 3:1 to 0.3:1, preferably from 2:1 to 0.5:1, in particular from1.5:1 to 0.66:1.

Reaction solutions which can be reacted according to variant (d)comprise one or more di- or polyhydroxycarboxylic acids containing atleast 2 hydroxyl groups per molecule, examples being dimethylolpropionicacid, dimethylolbutyric acid, tartaric acid, 3,4-dihydroxyhydrocinnamicacid, 2,3-dihydroxybenzoic acid, 2,4-dihydroxybenzoic acid,2,5-dihydroxybenzoic acid, 3,4-dihydroxybenzoic acid, and2,6-dihydroxybenzoic acid, or mixtures thereof.

Reaction solutions which can be reacted according to variant (e)comprise one or more hydroxydi- or hydroxypolycarboxylic acids, examplesbeing tartaric acid, citric acid, maleic acid, 4-hydroxyphthalic acid,2-hydroxyterephthalic acid or mixtures thereof.

The di- or polyhydroxycarboxylic acids and, respectively, hydroxydi- orhydroxypolycarboxylic acids from variants (d) and (e) may be used eitherper se or else in the form of derivatives.

By derivatives of di- or polyhydroxycarboxylic acids and, respectively,hydroxydi- or hydroxypolycarboxylic acids used in reaction solutionsaccording to variants (d) and (e) are meant preferably

-   -   the corresponding anhydrides in monomeric, dimeric or polymeric        form,    -   cyclic dimerization products,    -   esters with other carboxylic acids, such as with acetic acid,    -   monoalkyl or dialkyl esters, preferably monomethyl or dimethyl        esters or the corresponding monoethyl or diethyl esters, but        also the esters derived from higher alcohols such as n-propanol,        isopropanol, n-butanol, isobutanol, tert-butanol, n-pentanol,        and n-hexanol, for example,    -   monovinyl and divinyl esters, and    -   mixed esters, preferably methyl ethyl esters.

In the context of the present invention it is likewise possible to usedi- or polyhydroxycarboxylic acids and, respectively, hydroxydi- orhydroxypolycarboxylic acids and one or more of their derivatives. It islikewise possible in the context of the present invention to use amixture of two or more different derivatives of one or more di- orpolyhydroxycarboxylic acids and, respectively, hydroxydi- orhydroxypolycarboxylic acids.

In the context of the present invention it is likewise possible to reactmixtures of at least two of the above reaction solutions of variants (a)to (e): for example, a mixture of a reaction solution according tovariant (a) with a reaction solution according to variant (d) or (e).

By reaction solution is meant, in the context of the present invention,in variants (a) to (c), the mixtures of

-   -   compounds carrying hydroxyl and carboxyl groups,    -   solvent,    -   and any additives.

In the case of variants (d) and (e) reaction solutions in the context ofthe present invention are the mixtures of

-   -   one or more di- or polyhydroxycarboxylic acids and,        respectively, hydroxydi- or hydroxypolycarboxylic acids or        corresponding derivatives    -   with solvent        and any additives.

A preferred procedure is to remove the water formed during the reaction,preferably by operating in the presence of a water remover additiveadded at the beginning of the reaction. Suitable examples include weaklyacidic silica gels, weakly acidic aluminum oxides, molecular sieves,especially 4 Å molecular sieve, MgSO₄, and Na₂SO₄. The use of stronglyacidic silica gels is likewise possible. Additionally, further waterremover can be added during the reaction, or water remover can bereplaced by fresh water remover.

The process of the invention is conducted in the presence of an enzyme.Preference is given to using lipases or esterases. Highly suitablelipases and esterases are, for example, from Burkholderia Alantarii,Candida cylindracea, Candida lipolytica, Candida rugosa, Candidaantarctica, Candida utilis, Chromobacterium viscosum, Geotrichumviscosum, Geotrichum candidum, Mucor javanicus, Mucor mihei, pigpancreas, Pseudomonas spp., Pseudomonas fluorescens, Pseudomonascepacia, Rhizopus arrhizus, Rhizopus delemar, Rhizopus niveus, Rhizopusoryzae, Aspergillus niger, Penicillium roquefortii, Penicilliumcamembertii or esterase from Bacillus spp. and Bacillusthermoglucosidasius. Particular preference is given to Candidaantarctica Lipase B. The enzymes listed are available commercially, fromNovozymes Biotech Inc., Denmark, for example.

The enzyme is preferably used in immobilized form, on silica gel orLewatit®, for example. Methods of immobilizing enzymes are known per sefrom, for example, Kurt Faber, “Biotransformations in organicchemistry”, 3rd Edition 1997, Springer Verlag, section 3.2“Immobilization” pages 345–356. Immobilized enzymes are availablecommercially, from Novozymes Biotech Inc., Denmark, for example.

The amount of immobilized enzyme used is from 0.1 to 20% by weight, inparticular 10–15% by weight, based on the mass of all of the reactionstarting materials used.

The process of the invention is conducted at temperatures above 60° C.It is preferred to operate at temperatures of 100° C. or below.Preference is given to temperatures up to 80° C., with very particularpreference from 62 to 75° C., and more preferably still from 65 to 75°C.

The process of the invention is conducted in the presence of a solvent.Suitable examples include hydrocarbons such as paraffins or aromatics.Particularly suitable paraffins are n-heptane and cyclohexane.Particularly suitable aromatics are toluene, ortho-xylene, meta-xylene,para-xylene, xylene isomer mixture, ethylbenzene, chlorobenzene, andortho- and meta-dichlorobenzene. Further especially suitable solventsinclude ethers such as dioxane or tetrahydrofuran, for example, andketones such as methyl ethyl ketone and methyl isobutyl ketone, forexample.

The amount of solvent added is at least 5 parts by weight, based on themass of the reaction starting materials used, preferably at least 50parts by weight, and with particular preference at least 100 parts byweight. Amounts of more than 10,000 parts by weight of solvent areundesirable since at markedly lower concentrations the rate of reactionsubsides considerably, leading to uneconomically long reaction times.

The process of the invention is conducted at pressures above 500 mbar.It is preferred to react at atmospheric pressure or slightly elevatedpressure, up to 1200 mbar for example. It is also possible to operateunder considerably increased pressure, examples being pressures up to 10bar. Reaction at atmospheric pressure is preferred.

The reaction time of the process of the invention is normally from 4hours to 6 days, preferably from 5 hours to 5 days, and with particularpreference from 8 hours to 4 days.

After the end of the reaction the highly functional hyperbranchedpolyesters can be isolated, for example, by filtering off the enzyme andconcentrating the filtrate, normally under reduced pressure. Furtherhighly suitable workup methods are precipitation following addition ofwater, and subsequently washing and drying of the precipitate.

The present invention further provides the highly functionalhyperbranched polyesters obtainable by the process of the invention.They are distinguished by low levels of discoloration andresinification. On the definition of hyperbranched polymers see also P.J. Flory, J. Am. Chem. Soc. 1952, 74, 2718 and A. Sunder et al., Chem.Eur. J. 2000, 6, No. 1, 1–8. In the context of the present invention,however, “highly functional hyperbranched” means that there is onebranch with one functional group in at least 20 mol % of each secondmonomer unit in the case of variants (a) to (c) and one branch with afunctional group in every monomer unit in the case of variants (d) and(e).

The polyesters of the invention have a molecular weight M_(n) of from1000 to 30,000 g/mol, preferably from 2000 to 20,000 g/mol, withparticular preference from 3000 to 7000 g/mol, and with very particularpreference 4000 g/mol. The polydispersity is from 1.2 to 50, preferablyfrom 1.4 to 40, with particular preference from 1.5 to 30, and with veryparticular preference up to 10.

The highly functional hyperbranched polyesters of the invention arecarboxy-terminated, carboxy- and hydroxyl-terminated, and, preferably,hydroxyl-terminated and can be used with advantage for preparing, forexample, adhesives, coatings, foams, coverings, and paints.

The present invention additionally provides for the use of the highlyfunctional hyperbranched polyesters of the invention for preparingpolyadducts or polycondensates, examples being polycarbonates,polyurethanes, polyethers, and linear polyesters. It is preferred to usethe hydroxyl-terminated highly functional hyperbranched polyesters ofthe invention for preparing polyadducts or polycondensates, such aspolycarbonates or polyurethanes, for example.

The present invention further provides for the use of the highlyfunctional hyperbranched polyesters of the invention and of thepolyadducts or polycondensates prepared from highly functionalhyperbranched polyesters as a component of adhesives, coatings, foams,coverings, and paints. The present invention additionally providesadhesives, coatings, foams, coverings, and paints comprising the highlyfunctional hyperbranched polyesters of the invention or polyadducts orpolycondensates prepared from the highly functional hyperbranchedpolyesters of the invention. They are distinguished by outstandingperformance properties.

The invention is illustrated by examples.

EXAMPLE 1

In a 1 L round-bottomed flask 105.2 g (0.72 mol) of adipic acid and 55.2g (0.60 mol) of glycerol were dissolved in absolute dioxane (300 g).Molecular sieve (30 g, 0.4 nm) was then added, followed by immobilizedlipase from Candida antarctica B (Novozym® 435, 20 g). The reactionmixture was stirred under atmospheric pressure at 70° C. for 95 h. Itwas then cooled to room temperature and the enzyme was filtered off.Removal of the solvent under reduced pressure gave 138 g of a colorlessviscous oil which dissolved readily in THF.

-   M_(n)=3180 g-   M_(w)=30052 g-   Acid number: 42 mg KOH/g-   Polydispersity: 9.5, determined by gel permeation chromatography    with polystyrene calibration

EXAMPLE 2

In a 100 mL round-bottomed flask 6.78 g of azelaic acid (36 mmol) and2.76 g of glycerol (30 mmol) were reacted with one another in 40 g ofabsolute dioxane in the presence of Novozym® 435 (1.5 g) and molecularsieve (4 g, 0.4 nm). After 5 days of stirring at 70° C. the reactionmixture was cooled to room temperature, the enzyme was filtered off andthe solvent was distilled off under reduced pressure. This gave 7.9 g ofa colorless oil which dissolved readily in THF.

-   M_(n)=4743 g-   M_(w)=8614 g-   Acid number: 161 mg/KOH/g-   Polydispersity: 1.8

EXAMPLE 3

In a 100 mL round-bottomed flask 25.1 g of dimethyl adipate (144 mmol)and 11.1 g of glycerol (120 mmol) were reacted in absolute THF (20 mL)with addition of Novozym® 435 (5 g) and molecular sieve (30 g, 0.4 nm)at 70° C. under atmospheric pressure. After 5 days the reaction mixturewas cooled to room temperature, the enzyme was filtered off and thesolvent was distilled off under reduced pressure. This gave 20.5 g of acolorless oil which dissolved readily in THF.

-   M_(n)=8630 g-   M_(w)=91.743 g-   Acid number: 6.2 mg/KOH/g-   Polydispersity: 1.1

1. A process for preparing highly functional hyperbranched polyesterswhich comprises reacting a reaction solution comprising solvent and (a)one or more dicarboxylic acids or one or more derivatives thereof withone or more at least trifunctional alcohols (b) or one or moretricarboxylic acids or higher polycarboxylic acids or one or morederivatives thereof with one or more diols (c) or one or moretricarboxylic acids or higher polycarboxylic acids or one or morederivatives thereof with one or more at least trifunctional alcohols (d)or one or more di- or polyhydroxycarboxylic acids (e) or one or morehydroxydi- or hydroxypolycarboxylic acids or mixtures of at least two ofthe above reaction solutions in the presence of an enzyme attemperatures in the range from 62 to 75° C. and pressures above 500mbar.
 2. A process as claimed in claim 1, wherein water formed duringthe reaction is removed.
 3. A process as claimed in claim 1, wherein theenzyme is a lipase.
 4. A process as claimed in claim 1, wherein thelipase is Candida antarctica lipase B.
 5. A process as claimed in claim1, wherein the enzyme is used in immobilized form.
 6. A process asclaimed in claim 1, carried out at temperatures above 60° C. up to 80°C.
 7. A process as claimed in claim 1, wherein said derivatives of thedi-, tri- or polycarboxylic acids are the respective methyl or ethylesters.